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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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CHAPTER XXm
GLACIATION OF THE PRINCE WILLIAM SOUND AND LOWER COPPER
RIVER REGIONS
INTRODUCTORY
This chapter will be devoted to a discussion of some of the phenomena of general glaciation of the Prince William Sound and lower Copper River regions, except as already taken up in connection with individual glaciers and separate fiords. As in the corresponding discussion for the Yakutat Bay region (pp. 198-281), there will be amplification of special topics, but no attempt will be made to summarize the phenomena of glaciation presented in (pp. 82-450), except as they furnish evidence on the problems under consideration.1
The Copper River canyon will be dealt with first, then Princ6 William Sound, and, lastly, there will be a brief comparison of the glacial history of the Prince William Sound and Yakutat Bay regions.
THE LOWER COPPER RIVER
The Canyon Between Chitina and Tasnuna Rivers. From the broad intermontane basin of Copper and Susitna Rivers, which is surrounded by the Chugach, Wrangell, Talkeetna, and Alaska Ranges there are water-gaps and passes leading out in various directions. Copper River emerges at the lowest of these and plunges into the hundred miles of canyon by which this stream' crosses the Chugach Coast Range to the Pacific Ocean. This canyon consists of three quite different portions, (1) a northern, narrow canyon, (2) a wider, middle canyon, and (S) a southern, terminal portion which flares open toward the ocean. The northern, narrow portion of this canyon lies between the Chitina and Tasnuna Rivers, Its topography is shown in Figs. 69, 70, and PI. CLXXIX.
From the Chitina River southward (Fig. 69) the river valley at first narrows downstream (PL CLXXVI, A), the valley walls become higher, and the river plunges into Wood Canyon, a short, narrow, steep-walled gorge (PI. CLXXVI, B).
Below Wood Canyon the river is in a broader, young, stream valley, whose walls rise still higher as the stream penetrates the mountains, until, near Spirit Mountain and Tiekel River, elevations of 6000 to 7000 feet are attained within 2 miles of the river. It is, thus, even deeper than the Grand Canyon of the Colorado River in Arizona, but differs from it in having a form produced by glacial erosion. With this general character (PI. CLXXV) the canyon continues southward to Tasnuna River. Its grandeur is not seen as well from the railway, which follows the western bank, as from
1 For general maps of the area discussed see A. H. Brooks, Fl. 5, House Doc. 1846, Fart 2, 62nd Congress, 3rd session, Washington, 1913; U. S. Grant and D. F. Biggins, Fl. n, in pocket, Bull 443, U. S. Geol. Survey, 1910; and Map 1, in pocket of this book.
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